(i) Combination of cells in series:
In this combination, the cells are so connected that the negative terminal of one cell is connected to the positive terminal of the other cell such that in the end one free positive and one free negative terminal are left. These free terminals are connected to the external circuit. If the e.m.f of each cell is E and Y be the internal resistance and I be the current, then e.m.f. of the cell in series = nE (here n = 3) The total internal resistance = nr and External resistance = R
This shows that it is advantageous to connect cells in series to get a large current when their internal resistance is negligible. (ii) Combination of cells in parallel: Let there be n cells, each of e.m.f. E and internal resistance r, be connected in parallel as shown in the diagram. Total e.m.f. across the point A and B is E
It is advantageous to join cells in parallel when the internal resistance of each cell is quite high as compared to the external resistance R.
